To measure plasma concentrations of MPA and adjust CellCept doses to maintain plasma MPA concentrations in a proven-effective range. The goals are to: 1. Determine the variance of MPA AUC when dosage adjustments are made using MPA AUC vs. MPA pre-dose concentration. 2. Determine whether CellCept dose changes based on MPA plasma concentrations will reduce the risk of rejection. 3. Compare Afro-American MPA PK to Caucasian MPA PK.